It looks very well-done, and for the most part, it's a believable landscape. My only gripe is with some of your rivers. You may not be going for realism here, but most rivers naturally flow from north to south (Don't ask why, but with the exception of the Nile, it's rare to find a river going the other direction). And while it's not impossible, the river running through your southernmost island is a little weird to me. Over time, it would cause the mainland to split since the water doesn't come from a source.
Other than that, though (and it's really not too big of a deal), I dig it.